The metadata parameter stores additional, structured information on an object. You can use the
metadata parameter to attach key-value data to the following Digital River resources: SKUs, Checkouts, Orders, Customers, Returns, Refunds, and Fulfillments.
For example, you can store your user's full name and ID on a Digital River Customer object. Digital River does not use the metadata. Your users will only see this data if you choose to show it to them.
metadata parameter supports up to 20 keys. Each key name can be up to 40 characters long, and the values can be up to 500 characters long.